inverted wings & things

[velocity200]

Greetings from Australia......Gentlemen, I have been involved long term at an amateur level in a motorsport termed "landspeed racing" also known as time trials, the aim of this sport is to design a vehicle and race against the clock with the aim of achieving the highest average speed over a timed mile distance.
I have embarked on a new project who's goals are to exceed 500kph on a modified motorcycle, among the many challenges involved in achieving this is traction or in this case a distinct lack of it, the racing surface is salt( a large salt lake ) where the coefficient of friction ranges between 0.4 to 0.6. The solution for many is to simply add weight to increase the traction, but due to several constraints this is not feasible ( tyre load ratings and physical limits space to house the weight (lead)) so I am looking at using aerodynamic down force to achieve the needed traction.
Searching the literature and web I have found that it is considered possible at least in theory but there are very few examples of it having been performed in practice.
So gentlemen I require assistance in ascertaining how one should proceed in applying inverted wings and /or ground effects to a motorcycle. Caveat the vehicle will be maintaining a straight line of acceleration so no corners or leaning involved except for small roll and yaw movements due to relative wind speed and direction.

Cheers

 

[3DDave]

Weight transfer due to drag is caused by Q*Cd*(basis area)*(height of Center of pressure), where Q = (1/2)*rho*V^V

guessing 6 ft^2 for area; .00238 slug/ft^3 for rho, 300mph; Cd.5; height 1.5 ft; around 1040 ft-lbf of overturning moment on 700 lbf of drag. On a 6ft wheelbase, this will remove about 90 lbf from the front and add 90lbf to the rear.

at 300 mph, 700 lbf of drag requires 560 hp - so those number match.

700/.4 = about 1730 lbf of normal load on rear tire to provide traction under low traction levels. Something is off in your calculation of load to provide traction, plus kinda close on load limit for one tire.

I think fixing the wing in tilt is sufficient. If the wing is gimbaled to allow for bike tilt, how is the tilt measured and communicated to the wing?

Downforce is easier - as the suspension compresses under the wing-load the wing angle of attack can be tweaked by the motion of the suspension. At zero speed the wing can be at a full-lift stop.


The crosswind consideration is that one wing get more breeze than the other due to apparent yaw. At 300, 6mph isn't much but it's enough to notice.

 

[btrueblood]

"though that suggestion has so far been deemed too expensive by other speed teams (like hydroplanes). "

Sorry, not quite true as I wrote it. Hydroplanes do use an active forward canard wing, but the control of the canard angle-of-attack is left to the driver (typically drivers will add nose lift in the straightaways, and reduce lift for cornering). My suggestion is really that the lifting surface control should be at least partly done by a fly-by-wire computer, with the computer able to override pilot/driver inputs if/when the overturning moment limits are approached.

 

[rb1957]

this is drag due to the body, right? and there'll be induced drag from the wings, yes?

this is saying you need 1730 lbs down on the rear tire; 90 lbs down comes from the aero drag, something like 600 lbs from weight of bike, so you're looking for something like 1000 lbs from the wing, at 300mph = 440ft/sec ... 4ft2 with CL = 1, (20ft2 with CL = 0.2), 1 ft chord, 2*2ft span ... doesn't sound silly. mind you, this neglects that slower airflow near the body.

also the downforce is parabolic, i'd check some intermediate points to make sure you have the down load you expect/wnt. for example at 150 mph, you'd have only 250 lbs aero load ... enough ?

Quando Omni Flunkus Moritati

 

[3DDave]

Just to mention: in the traction calculation there needs to be a safety factor. Going 300mph flies in the face of a safety factor, but there should be one anyway.

 

[140Airpower]

"What is the difference between the force of gravity and the aerodynamic force of a wing? The only one I can see is that the wing will create drag."

... drag that increases the amount of downforce needed in addition to lowering the terminal velocity. This is why you should use weight instead of aero to produce the downforce IF YOU CAN and with the caveat that the acceleration run requirement is affect by the additional weight.

 

[imcjoek]

Make the front wheel drive too?

I assume there are rules against that...?